US3247297A

US3247297A - Process for the preparation of metallic materials by compression of a magnesium or magnesium alloy powder

Info

Publication number: US3247297A
Application number: US165035A
Authority: US
Inventors: Salesse Marc; Herenguel Jean; Caillat Roger; Boghen Jacques; Darras Raymond
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1961-03-03
Filing date: 1962-01-08
Publication date: 1966-04-19
Anticipated expiration: 1983-04-19
Also published as: DK110025C; SE209881C1; ES273932A1; LU41034A1; CH410437A; GB963605A; BE612189A; FR1292322A

Description

United States Patent 3 247 297 raocnss roa THE PfiErARA'rIoN "or METALLIC MATERIALS BY COMPRESSIQN OF A MAGNE- SIUM 0R MAGNESIUM ALLOY POWDER Marc Salesse, Gif sur Yvette, Jean Herenguel, Versailles,

Roger Caillat, Sevres, Jacques Boghen, Argenteuil, and

Raymond Darras, Versailles, France, assignors to Commissariat a lEnergie Atomique, Paris, France N0 Drawing. Filed .Ian. 8, 1962, Ser. No. 165,035

Claims priority, application France, Mar. 3, 1961, 854,486 7 Claims. (Cl. 264-82) The present invention relates to a process for the preparation of metallic materials by compression of a magnesium or magnesium alloy powder.

The invention also relates to powders and materials obtained by this process.

It is well known that the fields of use of metallic materials depend essentially upon their mechanical properties and their resistance to oxidation Within a given temperature range. In the case of magnesium and its alloys, a degradation of the mechanical properties of materials made from such metal occurs from about 350- 400 C. On the other hand, oxidation in air becomes very appreciable and rapidly accelerates when the temperature rises above 350-400 C., for example, the metal is completely unusable in dry or humid oxidising atmospheres or in a non-oxidising but humid medium.

Known processes for improving the mechanical resistance of magnesium generally consist in utilising alloys or, preferably, in making magnesium materials from powders which undergo oxidation before, during and/or after compaction of the powder.

Oxidation of magnesium particles is a very difficult operation, however, particularly with those fine powders which confer a high mechanical resistance on the material. This also applies to the fine parts of mixtures of powders of a range of particle sizes. With such fine powders, oxidation produces quite thick oxide films, if it does not cause, through uncontrollable elevation of the temperature, substantially complete oxidation which involves the risk of extending to the entire mass. The products obtained have the following disadvantages:

(a) Insufliciently high rupture load, due to the impossibility of using sufliciently fine powders;

'(b) Low rupture elongations in traction, both in the cold and hot, due to excessive general or local oxidation;

(0) Irregular and dispersed properties when the heating of the powders has not been suflicient before compaction;

(d) No improvement in the oxidation resistance.

The present invention has the object of providing an improved process for the preparation of magnesium-base materials which avoids these disadvantages and permits such materials to be obtained from magnesium or magnesium alloy powders. The materials produced have excellent mechanical properties, both in the cold and hot, and also have excellent resistance to corrosion at elevated temperatures in oxidising and humid atmospheres.

According to the invention, a process for the preparation of a magnesium-base material comprises compressing a magnesium-containing powder before, during and/or after subjecting it to an atmosphere containing fluorine or a fluorine compound at a temperature in the range of 0 to 600 C. so as to produce a compact material containing 0.1 to 15% by weight of combined fluorine.

The substance or substances which can be used, in carrying out the process, to incorporate the fluorine into the ultimate product, which is referred to for brevity as fluorina-tion," can include gaseous fluorine, hydrogen fluoride, hydrofluoric acid or any other fluorinated substance capable of readily evolving fluorine, and can if desired be diluted with an inert gas, such as argon.

The particle size range of the initial powder can be from 1 to 2000 microns. The process can be applied to powders having particles of any shape, such as spheres or dendrites, and also to powders having particles of very irregular shapes and sizes.

The temperature at which fluorination is carried out preferably lies between the ambient temperature and 600 C.

The duration of the fluorination step depends upon the composition of the gaseous phase used and also upon the temperature, and is generally from 2 to 5 hours.

The fluorination step can be effected in various ways.

A first preferred embodiment consists in introducing the powder to be fluorinated, before it is compacted into a receptacle made of suitable material, such as nickel or stainless steel, and placing the receptacle inside a sealed and fixed horizontal furance, made of a suitable material such as copper.

The apparatus is then purged with an inert gas, for example argon, and then gaseous fluorine or a fluorine compound, diluted with an inert gas if desired, is introduced. The introduction of the gas and, if desired, the temperature of heating are so controlled that the temperature lies between the ambient temperature and 600 C.

Another embodiment, in which fluorination is also eflected before compaction, consists in using a rotary furnace containing balls. In this case, the powder is continuously eroded as it is fluorinated. The balls can be of an appropriate material, such as steel covered with magnesium.

This process allows very fine particles to be obtained and lower temperatures to be used, for a given ombined fluorine content, as compared with the first embodiment. Also, the subsequent compaction of the treated powder more readily yields a material having good mechanical properties.

The fluorination treatment can also be eflected upon a compressed material obtained from the powder while subjecting the material to plastic deformation, for example rolling or drawing.

A fluorination agent can also be reacted with a more or less compact mass formed previously by compression of the powder. The mass can be produced by compression in the cold or at an elevated temperature. Either a non-fluorinated compacted powder or one previously compressed can be treated in the process.

Irrespective of the procedure adopted, a thin coating of magnesium fluoride is obtained on the metal particles, having a thickness of about one hundredth of a micron. The combined fluorine content of the metal should be controlled so as to have a value from 0.1 to 15% by weight in the final product. For a given sample of powder, the fluorine content which allows given mechanical properties to be obtained is a function of the particle size of the powder. With fine powders, having a particle size below 60 microns, the combined fluorine content preferably lies between 0.5 and 2%, if good ductiltiy with flow resistance are to be obtained.

In general, as the particle size of the powder increases the value of the rupture load decreases, while the rupture elongation value increases. For a powder of given particle size, increase in the fluorine content has the eflect of very slightly increasing the rupture load value and greatly decreasing the rupture elongation value. Use of the process of the invention consequently allows predetermined mechanical properties to be obtained, by varying the particle size of the powder or the fluorine content or both.

Compaction of the fluorinated powders is preferably carried out in several stages:

Table Particle size range of magnesium 10-65 10-65 10-65 5-40 Composite powder (microns). Mg-MgO material, 100-200 Specific surface (mi/g.) 0. 25 0.25 0. 25 0. 50

Typo of treatment Hydrogen Gaseous Gaseous Gaseous No fiuorinatluoride, 1 fluorine, 2 fluorine, 2 fluorine, 2 tion hr. at 290 hrs. at 330 hrs. at 475 hrs. at 475 treatment 0. C. O. C.

Fluorine content as percent by weight of product obtained 0.88 2 6 12 Thickness of fluorine on each grain (mircons) 0.02 0.05 0. 14 0. 14

Average mechanical properties at 20 C.

R, kgJmm. 33. 7 32. 3 34. 8 35 28 E, kg./mm. 31. 4 30. 6 33.1 34. 21 A percent (elongation) [V678 4. 5 3. 6 2. 01 1. 4 3 A (Brinell hardness) 57. 5 53. 4 59 69 47 Average mechanical properties at; 450 C.

R, k.g/mm. 1.65 2.03 2.6 2. 8 1. 2 K, kg./mm. 1. 4 1. 75 2. 2 2. 5 1 A percent (elongation)/; 67S 13. 5 13. 9 10. 5 4. 3 4

Firstly, compression is effected in the cold with a compressive force of 4 to 60 metric tons/mm With low compressions, it is advantageous first to place the powder within an auxiliary container of magnesium.

One or more compressions in the hot are then eiiected, depending upon the particle size range of the powder used, at temperatures below 600C. If the powders have particle sizes below 100 microns, two or three successive compressions at increasing temperatures are of advantages, since if compression at the maximum temperature were effected immediately after cold compression, oxidation would occur or even ignition of the magnesium powder.

The compressed materials so obtained can then be subjected to plastic deformation by the standard techby heating in air.

All the powder samples were subjected, after fluorination to a compaction treatment effected in a drawing mill having a drawing die ratio, S/s, of 49, with a compressive force of 40 metric tons/mm. The four following stages were employed.

' (a) Compression in the cold;

(b) Compression at 350C.; (0) Compression at 450C.;

(d) Compression at 500C.

By way of comparison, the right-hand column of the table shows the results obtained for a material prepared by the above compaction treatment, starting with a non- ;fiuorinated composite Mg-MgO material, having a particle size range of 100-200 microns. The material obtained was taken up to 450C. by heating in air. It may be mentioned in this connection that, if a very fine Mg-MgO powder is used, having a particle size range of 10 to 65 The table shows the improvement in mechanical properties which can be obtained by using the process of the invent-ion. The rupture load, elasticity and rupture elongation values, both cold and hot, are clearly better than the corresponding values of known magnesium-base materials, such as magnesium alloys or composite materials of the Mg-MgO type.

Apart from the mechanical properties described above, the fluorinated and compacted materials of the invention are of great interest because of their remarkable resistance to corrosion in air. They can be heated to 500 C. in air saturated with water vapour Without appreciably corroding, the increase in weight being less than 1 mg./ cm. after exposure for 800 hours, whereas with ordinary magnesium-base materials a very large degradation occurs in air at 400 C. and, from 350 C., oxidation is very substantial and can have serious effects.

The ignition temperature in humid air of the novel material is 640 C. and is about 40 to 50 C. higher than that of pure magnesium and undergoes much less violent combustion.

The process of the invention thus yields a novel material which is of particular interest in use in view of the following advantages:

(a) Mechanical properties in the cold and, particularly, in the hot, which are greatly superior to those of ordinary magnesium-base materials;

(b) Possibility of obtaining very varied mechanical properties as required, by varying either or both of the particle size range and the shape of the particles of the initial powder or the combined fluorine content, particularly by varying the temperature and/or duration of the treatment and the composition of the gaseous phase used;

(c) Resistance to oxidation by air, even humid, which is greatly improved at elevated temperatures, permitting use of magnesium up to a temperature of about 500 C., whereas operation was previously limited to below about Such characteristics have never previously been obtained and make the new material particularly suitable for use as a cladding material for fuel elements in nuclear reactors operating at high temperatures.

What is claimed is:

1. A process for the preparation of an improved metall'ic material formed from the compression of a member selected from the group consisting of a magnesium powder and a magnesium alloy powder comprising the steps of subjecting particles of said powder having a size range of from 1 to 2,000 microns to a gaseous atmosphere consisting essentially of a fluorine containing gas at a temperature from 0 C. to 600 C. until a material containing 0.1 to 15% by weight of combined fluorine as a thin film of magnesium fluoride on the particles is produced and compressing said particles of powder.

2. A process according to claim 1, in which the atmosphere contains the fluorination agent and an inert gas.

3. A process according to claim 1, in which the fluorination agent is fluorine.

4. A process according to claim 1, in which the fluorination agent is hydrogen fluoride.

5. A process according to claim 1, in which the powder is first subjected to the action of the fluorination atmosphere for a time sufficient to attain the desired degree of fluorination of the metal-containing powder and is then compressed.

6. A process according to claim 1, in which heating is effected for a period of 2 to 5 hours.

7. A magnesium-base material comprising a powder, the particles of which comprise substantially magnesium,

have a size range from 1 to 2,000 microns and are covered with a thin coating of magnesium fluoride, the combined fluorine content of the coated metal particles being between 0.1 to 15% by weight.

References Cited by the Examiner OTHER REFERENCES Metals Handbook, volume 1, American Society for Metals, Metals Park, Ohio, 1961. TA 472 A3, pages 1095-1111.

LEON D. ROSDOL, Primary Examiner.

RAY K. WINDHAM, CARL D. QUARFORTH,

Examiners.

A. I. MUCCINO, R. L. GOLDBERG, R. L. GRUD- ZIECKI, Assistant Examiners.

Claims

1. A PROCESS FOR THE PREPARATION OF AN IMPROVED METALLIC MATERIAL FORMED FROM THE COMPRESSION OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF A MAGNESIUM POWDER AND A MAGNESIUM ALLOY POWDER COMPRISING THE STEPS OF SUBJECTING PARTICLES OF SAID POWDER HAVING A SIZE RANGE OF FROM 1 TO 2,000 MICRONS TO A GASEOUS ATMOSPHERE CONSISTING ESSENTIALLY OF A FLUORINE CONATINING GAS AT A TEMPERATURE FROM 0* C. TO 600*C. UNTIL A MATERIAL CONTAINING 0.1 TO 15% BY WEIGHT OF COMBINED FLUORINE AS A THIN FILM OF MAGNESIUM FLUORIDE ON THE PARTICLES IS PRODUCED AND COMPRESSING SAID PARTICLES OF POWDER.